During operation of electrical machines, including permanent magnet electrical machines, generated heat, such as due to losses induced in the magnets from space and time harmonics, needs to be dissipated. For example, limited temperature capabilities and/or temperature sensitivity of the magnets used in permanent magnet machines means that heat dissipation should be sufficient to maintain the magnets within acceptable temperature ranges and/or limit temperature variations between parts and/or regions of the machine.
In electrical machines with solid rotors, the loss-generated heat may be conducted through the rotor to the rotor surface for dissipation by convection to the ambient or airgap air. However, the airgap air may be of a relatively high temperature such as to provide a limited route for heat dissipation, and the portions of the shaft that may be exposed to ambient air may have a relatively long and/or otherwise inefficient heat flow or conduction paths.
Examples of electrical machine rotors are disclosed in U.S. Pat. Nos. 4,028,573; 6,452,301 and 7,619,342; in International Publication Nos. WO2007/110282 and WO2011/012131; and in Japanese published patent application JP2006-158008A. Examples of composite shafts, armatures and tubes are disclosed in U.S. Pat. Nos. 3,623,220; 5,851,152; 6,072,252; 7,323,509 and 7,617,582; and in European Patent Application Publication No. 0577409A1. The disclosures of these and all other publications referenced herein are incorporated by reference in their entirety for all purposes.